Three-dimensional network aluminum porous body, electrode using the aluminum porous body, and nonaqueous electrolyte battery, capacitor and lithium-ion capacitor with nonaqueous electrolytic solution, each using the electrode

ABSTRACT

A three-dimensional network aluminum porous body which enables to produce an electrode continuously, an electrode using the aluminum porous body, and a method for producing the electrode. A long sheet-shaped three-dimensional network aluminum porous body is provided to be used as a base material in a method for producing an electrode including at least winding off, a thickness adjustment step, a lead welding step, an active material filling step, a drying step, a compressing step, a cutting step and winding-up, wherein the three-dimensional network aluminum porous body has a tensile strength of 0.2 MPa or more and 5 MPa or less.

TECHNICAL FIELD

The present invention relates to a three-dimensional aluminum porousbody which is used for a nonaqueous electrolyte battery (lithiumbattery, etc.), and a capacitor (hereinafter, simply referred to as a“capacitor”) and a lithium-ion capacitor (hereinafter, simply referredto as a “lithium-ion capacitor”) with a nonaqueous electrolyticsolution, and an electrode using the three-dimensional network aluminumporous body, and a method for producing the electrode.

BACKGROUND ART

Metal porous bodies having a three-dimensional network structure havebeen used in a wide range of applications, such as various filters,catalyst supports and battery electrodes. For example, Celmet(manufactured by Sumitomo Electric Industries, Ltd., registeredtrademark) composed of three-dimensional network nickel porous body(hereinafter, referred to as a “nickel porous body”) has been used as anelectrode material for batteries, such as nickel-metal hydride batteriesand nickel-cadmium batteries. Celmet is a metal porous body havingcontinuous pores and characteristically has a higher porosity (90% ormore) than other porous bodies such as metallic nonwoven fabrics. Celmetcan be obtained by forming a nickel layer on the surface of the skeletonof a porous resin molded body having continuous pores such as urethanefoam, then decomposing the resin molded body by heat treatment, andreducing the nickel. The nickel layer is formed by performing aconductive treatment of applying a carbon powder or the like to thesurface of the skeleton of the resin molded body and then depositingnickel by electroplating.

On the other hand, as with nickel, aluminum has excellentcharacteristics such as a conductive property, corrosion resistance andlightweight, and for applications in batteries, for example, an aluminumfoil in which an active material, such as lithium cobalt oxide, isapplied onto the surface thereof has been used as a positive electrodefor a lithium battery. In order to increase the capacity of a positiveelectrode, it is considered that a three-dimensional network aluminumporous body (hereinafter, referred to as an “aluminum porous body”) inwhich the surface area of aluminum is increased is used and the insideof the aluminum is filled with an active material. The reason for thisis that this allows the active material to be utilized even in anelectrode having a large thickness and improves the active materialavailability ratio per unit area.

As a method for manufacturing an aluminum porous body, Patent Literature1 describes a method of subjecting a three-dimensional network plasticsubstrate having an inner continuous space to an aluminum vapordeposition process by an arc ion plating method to form a metallicaluminum layer having a thickness of 2 to 20 μm.

It is said that in accordance with this method, an aluminum porous bodyhaving a thickness of 2 to 20 μm is obtained, but since this method isbased on a vapor-phase process, it is difficult to produce a large-areaporous body, and it is difficult to form a layer which is internallyuniform depend on the thickness or porosity of the substrate. Further,this method has problems that a formation rate of the aluminum layer islow and production cost is high since equipment for manufacturing isexpensive. Moreover, when a thick film is formed, there is a possibilitythat cracks may be produced in the film or aluminum may exfoliate.

Patent Literature 2 describes a method of obtaining an aluminum porousbody, including forming a film made of a metal (such as copper) on theskeleton of a resin foam molded body having a three-dimensional networkstructure, the metal having an ability to form a eutectic alloy at atemperature equal or below the melting point of aluminum, then applyingan aluminum paste to the film, and performing a heat treatment in anon-oxidizing atmosphere at a temperature of 550° C. or higher and 750°C. or lower to remove an organic constituent (resin foam) and sinter analuminum powder.

However, in accordance with this method, a layer which forms a eutecticalloy of the above-mentioned metal and aluminum is produced and analuminum layer of high purity cannot be formed.

As other methods, it is considered that a resin molded body having athree-dimensional network structure is subjected to aluminum plating. Anelectroplating process of aluminum itself is known, but since aluminumhas high chemical affinity to oxygen and a lower electric potential thanhydrogen, the electroplating in a plating bath containing an aqueoussolution system is difficult. Thus, conventionally, aluminumelectroplating has been studied in a plating bath containing anonaqueous solution system. For example, as a technique for plating ametal surface with aluminum for the purpose of antioxidation of themetal surface, Patent Literature 3 discloses an aluminum electroplatingmethod wherein a low melting composition, which is a blend melt of anonium halide and an aluminum halide, is used as a plating bath, andaluminum is deposited on a cathode while the water content of theplating bath is maintained at 2 mass % or less.

However, in the aluminum electroplating, plating of only a metal surfaceis possible, and there is no known method of electroplating on thesurface of a resin molded body, in particular electroplating on thesurface of a resin molded body having a three-dimensional networkstructure.

The present inventors have made earnest investigations concerning amethod of electroplating the surface of a resin molded body made ofpolyurethane having a three-dimensional network structure with aluminum,and have found that it is possible to electroplate the surface of aresin molded body made of polyurethane by plating the resin molded bodymade of polyurethane, in which at least the surface is made electricallyconductive, with aluminum in a molten salt bath. These findings have ledto completion of a method for producing an aluminum porous body. Inaccordance with this production method, an aluminum structure having aresin molded body made of polyurethane as the core of its skeleton canbe obtained. For some applications such as various filters and catalystsupports, the aluminum structure may be used as a resin-metal compositeas it is, but when the aluminum structure is used as a metal structurewithout resin because of constraints resulting from the usageenvironment, an aluminum porous body needs to be formed by removing theresin.

Removal of the resin can be performed by any method, includingdecomposition (dissolution) with an organic solvent, a molten salt orsupercritical water, decomposition by heating or the like.

Here, a method of decomposition by heating at high temperature or thelike is convenient, but it involves oxidation of aluminum. Sincealuminum is difficult to reduce after being oxidized once as distinctfrom nickel, if being used in, for example, an electrode material of abattery or the like, the electrode loses a conductive property due tooxidation, and therefore aluminum cannot be used as the electrodematerial. Thus, the present inventors have completed a method forproducing an aluminum porous body, in which an aluminum structureobtained by forming an aluminum layer on the surface of a resin moldedbody is heated to a temperature equal to or below the melting point ofaluminum in a state being dipped in a molten salt while applying anegative potential to the aluminum layer to remove the resin molded bodythrough thermal decomposition to obtain an aluminum porous body, as amethod of removing a resin without causing the oxidation of aluminum.

Incidentally, in order to use the aluminum porous body thus obtained asan electrode, it is necessary to attach a lead wire to the aluminumporous body to form a current collector, fill the aluminum porous bodyserving as the current collector with an active material, and subjectthe resulting aluminum porous body to treatments such as compressing andcutting by a process shown in FIG. 1, but a technology for practical usefor industrially producing electrodes for nonaqueous electrolytebatteries, capacitors or the like from an aluminum porous body has notyet been known.

CITATION LIST Patent Literatures

-   Patent Literature 1: Japanese Patent No. 3413662-   Patent Literature 2: Japanese Unexamined Patent Publication No.    8-170126-   Patent Literature 3: Japanese Patent No. 3202072-   Patent Literature 4: Japanese Unexamined Patent Publication No.    56-86459

SUMMARY OF INVENTION Technical Problem

The present invention aims at providing a technology for practical usefor industrially producing an electrode from an aluminum porous body,and specifically, it is an object of the present invention to provide athree-dimensional network aluminum porous body which enables to producean electrode continuously, an electrode using the aluminum porous body,and a method for producing the electrode.

Solution to Problem

The constitution of the present invention is as follows.

(1) A three-dimensional network aluminum porous body comprising a longsheet-shaped three-dimensional network aluminum porous body that is usedas a base material in a method for producing an electrode including atleast winding off, a thickness adjustment step, a lead welding step, anactive material filling step, a drying step, a compressing step, acutting step and winding-up, the three-dimensional network aluminumporous body having a tensile strength of 0.2 MPa or more and 5 MPa orless.

(2) The three-dimensional network aluminum porous body according to (1),wherein the three-dimensional network aluminum porous body has anaverage crystal grain size of 1 μm or more and 100 μm or less.

(3) The three-dimensional network aluminum porous body according to (1)or (2), wherein the three-dimensional network aluminum porous bodycontains carbon in an amount of 0.05 g/m² or more and 20 g/m² or less.

(4) A method for producing an electrode comprising at least winding off,a thickness adjustment step, a lead welding step, an active materialfilling step, a drying step, a compressing step, a cutting step andwinding-up, wherein the three-dimensional network aluminum porous bodyaccording to any one of (1) to (3) is used as a base material.

(5) An electrode, comprising using the three-dimensional networkaluminum porous body according to any one of (1) to (3).

(6) A nonaqueous electrolyte battery, comprising using the electrodeaccording to (5).

(7) A capacitor using a nonaqueous electrolytic solution, comprisingusing the electrode according to (5).

(8) A lithium-ion capacitor using a nonaqueous electrolytic solution,comprising using the electrode according to (5).

Advantageous Effects of Invention

Since the three-dimensional network aluminum porous body of the presentinvention is excellent in tensile strength, it does not break in aprocess of continuously producing an electrode material and thereforecan reduce the cost of industrial production.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view showing a process for producing an electrode materialfrom an aluminum porous body.

FIG. 2 is a view for illustrating a measuring method of an averagecrystal grain size of the aluminum porous body.

FIG. 3 is a flow chart showing a step of producing an aluminum structureaccording to the present invention.

FIGS. 4A, 4B, 4C and 4D are schematic sectional views illustrating astep of producing an aluminum structure according to the presentinvention.

FIG. 5 is an enlarged photograph of the surface of the structure of aresin molded body made of polyurethane.

FIG. 6 is a view illustrating an example of a step of a continuousconductive treatment of the surface of a resin molded body with aconductive coating material.

FIG. 7 is a view illustrating an example of a step of continuousaluminum plating utilizing molten salt plating.

FIG. 8 is a view showing a step of compressing an end part of analuminum porous body to form a compressed part.

FIG. 9 is a view showing a step of compressing the central part of analuminum porous body to form a compressed part.

FIG. 10 is a view showing a step of filling a porous part of an aluminumporous body with an active material slurry.

FIG. 11 is a schematic view showing an example of a structure in whichan aluminum porous body is applied to a lithium battery.

FIG. 12 is a schematic view showing an example of a structure in whichan aluminum porous body is applied to a capacitor.

FIG. 13 is a schematic view showing an example of a structure in whichan aluminum porous body is applied to a lithium-ion capacitor.

FIG. 14 is a schematic sectional view showing an example of a structurein which an aluminum porous body is applied to a molten salt battery.

DESCRIPTION OF EMBODIMENTS

The three-dimensional network aluminum porous body of the presentinvention is a long sheet-shaped three-dimensional network aluminumporous body to be used as a base material in a method for producing anelectrode including at least winding off, a thickness adjustment step, alead welding step, an active material filling step, a drying step, acompressing step, a cutting step and winding-up, wherein thethree-dimensional network aluminum porous body has a tensile strength of0.5 MPa or more and 5 MPa or less.

It is necessary to use a long sheet-shaped metal porous body in order toperform industrial continuous production of an electrode for anonaqueous electrolyte battery (lithium battery, etc.), and a capacitoror a lithium-ion capacitor. Therefore, the three-dimensional networkaluminum porous body of the present invention is has a feature of beinglong sheet-shaped in order to correspond to industrial continuousproduction of an electrode. That is, the shape of the three-dimensionalnetwork aluminum porous body of the present invention can beappropriately changed in response to a production line continuouslyproducing an electrode and may be a shape of a long sheet applicable tosuch a series of steps, and the dimension of the aluminum porous body isnot particularly limited. The dimension can be, for example, 1 m wide,200 m long and 1 mm thick.

Generally, in order to continuously produce an electrode, as shown inFIG. 1, a long sheet-shaped metal porous body needs to be wound off froma roll, undergo the respective steps, and be wound-up around a roll, andthe metal porous body is carried while being pulled by a constant forceduring the series of steps. Since the metal porous body is stronglypulled particularly in the filling step and the pressing step, the metalporous body has a problem of break if it does not have a certain levelof tensile strength. Accordingly, the three-dimensional network aluminumporous body of the present invention is has a feature of having atensile strength of 0.2 MPa or more and 5 MPa or less so that thethree-dimensional network aluminum porous body can be used for acontinuous production step of an electrode.

When the aluminum porous body has a tensile strength of less than 0.2MPa, there is a high possibility of break in the step of continuouslyproducing an electrode. On the contrary, when the tensile strength ismore than 5 MPa, it is not preferred since the aluminum porous bodybecomes hard to bend and cannot be wound-up in the form of a roll. Fromsuch viewpoints, the aluminum porous body more preferably has a tensilestrength of 0.2 MPa or more and 4 MPa or less, furthermore preferably0.3 MPa or more and 2.5 MPa or less, and most preferably 0.5 MPa or moreand 1.2 MPa or less.

In order to obtain an aluminum porous body having a tensile strength of0.2 MPa or more, the conditions (temperature, time, current, etc.) ofaluminum plating may be adjusted or the carbon content may be adjustedin the production step of the aluminum porous body described later.

Further, the three-dimensional network aluminum porous body of thepresent invention preferably has an average crystal grain size of 1 μmor more and 100 μm or less. When the aluminum porous body has an averagecrystal grain size of less than 1 μm, there may be cases where theductility of the porous body is decreased to cause the processability todeteriorate. On the contrary, when the average crystal grain size ismore than 100 μm, there may be cases where mechanical strength isreduced. From such viewpoints, the aluminum porous body more preferablyhas an average crystal grain size of 2 μm or more and 10 μm or less, andfurthermore preferably 3 μm or more and 8 μM or less.

The average crystal grain size of the aluminum porous body can beadjusted by adjusting the conditions (temperature, time, current, etc.)of aluminum plating in the production step of the aluminum porous bodydescribed later.

The average crystal grain size of the aluminum porous body can bemeasured by processing the aluminum porous body with an FIB (focused ionbeam), and then observing the aluminum porous body with an SEM (scanningelectron microscope). More specifically, in the photograph of analuminum porous body by the SEM shown in FIG. 2, for example, a linehaving the same length as that of a scale in the SEM photograph is drawnin the skeleton of the aluminum porous body, and the number of crystalgrains intersecting with the line is counted. A grain size is calculatedby dividing the length of the scale by the number of crystal grains((length of scale)/(number of crystal grains)). This procedure isrepeated at five different points in a photograph to calculate eachgrain size value, and an average of these values is taken as an averagecrystal grain size.

The three-dimensional network aluminum porous body of the presentinvention preferably contains carbon in an amount of 0.05 g/m² or moreand 20 g/m² or less. When the aluminum porous body contains carbon in anamount of 0.05 g/m² or more, the mechanical strength of the aluminumporous body can be enhanced. On the other hand, when the aluminum porousbody contains carbon in an amount of more than 20 g/m², it is notpreferred since processability of the aluminum porous body isdeteriorated to cause a high probability of being starting point ofcracking when being bent, Further, weldability of the aluminum porousbody may be deteriorated. From such viewpoints, the aluminum porous bodymore preferably contains carbon in an amount of 0.1 g/m² or more and 10g/m² or less, and furthermore preferably 0.2 g/m² or more and 5 g/m² orless.

As described later, in producing an aluminum porous body, the amount ofcarbon contained in an aluminum porous body as a final product can beadjusted by using a three-dimensional network resin molded body of aurethane foam or the like as a starting material and adjusting theconditions (temperature, time, etc.) of removing the resin molded body.

Hereinafter, a method for manufacturing the three-dimensional networkaluminum porous body of the present invention will be described.Hereinafter, the production method will be described with reference tothe drawings if necessary, taking an example in which an aluminumplating method is applied as a method of forming an aluminum film on thesurface of a resin molded body made of polyurethane for a representativeexample. Throughout the reference figures hereinafter, the partsassigned the same number are the same parts or the corresponding parts.The present invention is not limited thereto but is defined by theclaims, and all modifications which fall within the scope of the claimsand the equivalents thereof are intended to be embraced by the claims.

(Step of Producing Aluminum Structure)

FIG. 3 is a flow chart showing a step of producing an aluminumstructure. Further, FIGS. 4A, 4B, 4C and 4D show schematic views of theformation of an aluminum plating film using a resin molded body as acore material corresponding to the flow chart. The overall flow of theproduction step will be described with reference to both figures. First,preparation 101 of a resin molded body serving as a base material isperformed. FIG. 4A is an enlarged schematic view of the surface of aresin molded body having continuous pores as an example of a resinmolded body serving as a base material. Pores are formed in the skeletonof a resin molded body 1. Next, a conductive treatment 102 of thesurface of the resin molded body is performed. As illustrate in FIG. 4B,through this step, a thin conductive layer 2 made of an electricconductor is formed on the surface of the resin molded body 1.

Subsequently, aluminum plating 103 in a molten salt is performed to forman aluminum plated layer 3 on the surface of the conductive layer of theresin molded body (FIG. 4C). Thereby, an aluminum structure is obtainedin which the aluminum plated layer 3 is formed on the surface of theresin molded body serving as a base material. Removal 104 of the resinmolded body serving as the base material is performed.

The resin molded body 1 can be removed by decomposition or the like toobtain an aluminum structure (porous body) containing only a remainingmetal layer (FIG. 4D). Hereinafter, each of these steps will bedescribed in turn.

(Preparation of Resin Molded Body)

A resin molded body having a three-dimensional network structure andcontinuous pores is prepared. A material of the resin molded body may beany resin. As the material, a resin foam molded body made ofpolyurethane, melamine resin, polypropylene or polyethylene can beexemplified. Though the resin foam molded body has been exemplified, aresin molded body having any shape may be selected as long as the resinmolded body has continuously-formed pore (continuous pores). Forexample, a resin molded body having a shape like a nonwoven fabricformed by tangling fibrous resin can be used in place of the resin foammolded body. The resin foam molded body preferably has a porosity of 80%to 98% and a pore diameter of 50 μm to 500 μm. Urethane foams andmelamine resin foams have a high porosity, continuity of pores, andexcellent thermal decomposition properties and therefore they can bepreferably used as the resin foam molded body.

Urethane foams are preferred in points of uniformity of pores, easinessof availability and the like, and preferred in that urethane foams witha small pore diameter can be available.

Resin molded bodies often contain residue materials such as a foamingagent and an unreacted monomer in the production of the foam, and aretherefore preferably subjected to a washing treatment for the sake ofthe subsequent steps. As an example of the resin molded body, a urethanefoam subjected to a washing treatment as a preliminary treatment isshown in FIG. 5. In the resin molded body, a three-dimensional networkis configured as a skeleton, and therefore continuous pores areconfigured as a whole. The skeleton of the urethane foam has an almosttriangular shape in a cross-section perpendicular to its extendingdirection. Herein, the porosity is defined by the following equation:Porosity=(1−(mass of porous material[g]/(volume of porousmaterial[cm³]×material density)))×100[%]

Further, the pore diameter is determined by magnifying the surface ofthe resin molded body in a photomicrograph or the like, counting thenumber of pores per inch (25.4 mm) as the number of cells, andcalculating an average pore diameter by the following equation: averagepore diameter=25.4 mm/the number of cells.

(Conductive Treatment of Surface of Resin Molded Body)

In order to perform electroplating, the surface of the resin foam ispreviously subjected to a conductive treatment. A method of theconductive treatment is not particularly limited as long as it is atreatment by which a layer having a conductive property can be disposedon the surface of the resin molded body, and any method, includingelectroless plating of a conductive metal such as nickel, vapordeposition and sputtering of aluminum or the like, and application of aconductive coating material containing conductive particles such ascarbon, may be selected.

As an example of the conductive treatment, a method of making thesurface of the resin foam electrically conductive by sputtering ofaluminum, and a method of making the surface of the resin foamelectrically conductive by using carbon as conductive particles will bedescribed below.

—Sputtering of Aluminum—

A sputtering treatment using aluminum is not limited as long as aluminumis used as a target, and it may be performed according to an ordinarymethod. A sputtering film of aluminum is formed by, for example, holdinga resin molded body with a substrate holder, and then applying a directvoltage between the holder and a target (aluminum) while introducing aninert gas into the sputtering apparatus to make an ionized inert-gasimpinge onto the aluminum target and deposit the sputtered aluminumparticles on the surface of the resin molded body. The sputteringtreatment is preferably performed below a temperature at which the resinmolded body is not melted, and specifically, the sputtering treatmentmay be performed at a temperature of about 100 to 200° C., andpreferably at a temperature of about 120 to 180° C.

—Carbon Application—

A carbon coating material is prepared as a conductive coating material.A suspension liquid serving as the conductive coating materialpreferably contains carbon particles, a binder, a dispersing agent, anda dispersion medium. Uniform application of conductive particlesrequires maintenance of uniform suspension of the suspension liquid.Thus, the suspension liquid is preferably maintained at a temperature of20° C. to 40° C. The reason for this is that a temperature of thesuspension liquid below 20° C. results in a failure in uniformsuspension, and only the binder is concentrated to form a layer on thesurface of the skeleton constituting the network structure of the resinmolded body. In this case, a layer of applied carbon particles tends topeel off, and metal plating firmly adhering to the substrate is hardlyformed. On the other hand, when a temperature of the suspension liquidis higher than 40° C., since the amount of the dispersing agent toevaporate is large, with the passage of time of application treatment,the suspension liquid is concentrated and the amount of carbon to beapplied tends to vary. The carbon particle has a particle diameter of0.01 to 5 μm, and preferably 0.01 to 0.5 μm. A large particle diametermay result in the clogging of holes of the resin molded body orinterfere with smooth plating, and too small particle diameter makes itdifficult to ensure a sufficient conductive property.

The application of the carbon particles to the resin molded body can beperformed by dipping the resin molded body to be a subject in thesuspension liquid and squeezing and drying the resin molded body. FIG. 6is a schematic view showing the configuration of a treatment apparatusfor conductive treatment of a strip-shaped resin molded body (astrip-shaped resin), which is to serve as a skeleton, as an example of apractical production step. As shown in the figure, this apparatusincludes a supply bobbin 12 for feeding a strip-shaped resin 11, a bath15 containing a suspension liquid 14 of a conductive coating material, apair of squeezing rolls 17 disposed above the bath 15, a plurality ofhot air nozzles 16 disposed on opposite sides of the runningstrip-shaped resin 11, and a take-up bobbin 18 for taking up the treatedstrip-shaped resin 11. Further, a deflector roll 13 for guiding thestrip-shaped resin 11 is appropriately disposed. In the apparatus thusconfigured, the strip-shaped resin 11 having a three-dimensional networkstructure is unwound from the supply bobbin 12, is guided by thedeflector roll 13, and is dipped in the suspension liquid in the bath15. The strip-shaped resin 11 dipped in the suspension liquid 14 in thebath 15 changes its direction upward and runs through between thesqueezing rolls 17 disposed above the liquid surface of the suspensionliquid 14. In this case, the distance between the squeezing rolls 17 issmaller than the thickness of the strip-shaped resin 11, and thereforethe strip-shaped resin 11 is compressed. Thus, an excessive suspensionliquid with which the strip-shaped resin 11 is impregnated is squeezedout into the bath 15.

Subsequently, the strip-shaped resin 11 changes its running directionagain. The dispersion medium or the like of the suspension liquid isremoved by hot air ejected from the hot air nozzles 16 configured by aplurality of nozzles, and the strip-shaped resin 11 fully dried is woundaround the take-up bobbin 18. The temperature of the hot air ejectedfrom the hot air nozzles 16 preferably ranges from 40° C. to 80° C. Whensuch an apparatus is used, the conductive treatment can be automaticallyand continuously performed and a skeleton having a network structurewithout clogging and having a uniform conductive layer is formed, andtherefore, the subsequent metal plating step can be smoothly performed.

(Formation of Aluminum Layer: Molten Salt Plating)

Next, an aluminum-plated layer is formed on the surface of the resinmolded body by electroplating in a molten salt. By plating aluminum inthe molten salt bath, a thick aluminum layer can be uniformly formedparticularly on the surface of a complicated skeleton structure like theresin molded body having a three-dimensional network structure. A directcurrent is applied between a cathode of the resin molded body having asurface subjected to the conductive treatment and an anode of analuminum plate with a purity of 99.0% in the molten salt. As the moltensalt, an organic molten salt which is a eutectic salt of an organichalide and an aluminum halide or an inorganic molten salt which is aeutectic salt of an alkaline metal halide and an aluminum halide may beused. Use of an organic molten salt bath which melts at a relatively lowtemperature is preferred because it allows plating without thedecomposition of the resin molded body, a base material. As the organichalide, an imidazolium salt, a pyridinium salt or the like may be used,and specifically, 1-ethyl-3-methylimidazolium chloride (EMIC) andbutylpyridinium chloride (BPC) are preferred. Since the contamination ofthe molten salt with water or oxygen causes degradation of the moltensalt, plating is preferably performed in an atmosphere of an inert gas,such as nitrogen or argon, and in a sealed environment.

The molten salt bath is preferably a molten salt bath containingnitrogen, and particularly an imidazolium salt bath is preferably used.In the case where a salt which melts at a high temperature is used asthe molten salt, the dissolution or decomposition of the resin in themolten salt is faster than the growth of a plated layer, and therefore,a plated layer cannot be formed on the surface of the resin molded body.The imidazolium salt bath can be used without having any affect on theresin even at relatively low temperatures. As the imidazolium salt, asalt which contains an imidazolium cation having alkyl groups at1,3-position is preferably used, and particularly, aluminumchloride+1-ethyl-3-methylimidazolium chloride (AlCl₃+EMIC)-based moltensalts are most preferably used because of their high stability andresistance to decomposition. The imidazolium salt bath allows plating ofurethane foam resins and melamine resin foams, and the temperature ofthe molten salt bath ranges from 10° C. to 65° C., and preferably 25° C.to 60° C. With a decrease in temperature, the current density rangewhere plating is possible is narrowed, and plating of the entire surfaceof a resin molded body becomes difficult. The failure that a shape of abase resin is impaired tends to occur at a high temperature higher than65° C.

With respect to molten salt aluminum plating on a metal surface, it isreported that an additive, such as xylene, benzene, toluene or1,10-phenanthroline, is added to AlCl₃-EMIC for the purpose of improvingthe smoothness of the plated surface. The present inventors have foundthat particularly in aluminum plating of a resin molded body having athree-dimensional network structure, the addition of 1,10-phenanthrolinehas characteristic effects on the formation of an aluminum porous body.That is, it provides a first characteristic that the smoothness of aplating film is improved and the aluminum skeleton forming the porousbody is hardly broken, and a second characteristic that uniform platingcan be achieved with a small difference in plating thickness between thesurface and the interior of the porous body.

In the case of pressing the completed aluminum porous body or the like,the above-mentioned two characteristics of the hard-to-break skeletonand the uniform plating thickness in the interior and exterior canprovide a porous body which has a hard-to-break skeleton as a whole andis uniformly pressed. When the aluminum porous body is used as anelectrode material for batteries or the like, it is performed that anelectrode is filled with an electrode active material and is pressed toincrease its density. However, since the skeleton is often broken in thestep of filling the active material or pressing, the two characteristicsare extremely effective in such an application.

According to the above description, the addition of an organic solventto the molten salt bath is preferred, and particularly1,10-phenanthroline is preferably used. The amount of the organicsolvent added to the plating bath preferably ranges from 0.2 to 7 g/L.When the amount is 0.2 g/L or less, the resulting plating is poor insmoothness and brittle, and it is difficult to achieve an effect ofdecreasing a difference in thickness between the surface layer and theinterior. When the amount is 7 g/L or more, plating efficiency isdecreased and it is difficult to achieve a predetermined platingthickness.

FIG. 7 is a view schematically showing the configuration of an apparatusfor continuously plating the above-mentioned strip-shaped resin withaluminum. This view shows a configuration in which a strip-shaped resin22 having a surface subjected to a conductive treatment is transferredfrom the left to the right in the figure. A first plating bath 21 a isconfigured by a cylindrical electrode 24, an aluminum anode 25 disposedon the inner wall of a container, and a plating bath 23. Thestrip-shaped resin 22 passes through the plating bath 23 along thecylindrical electrode 24, and thereby a uniform electric current caneasily flow through the entire resin molded body, and uniform platingcan be achieved. A plating bath 21 b is a bath for further performingthick uniform plating and is configured by a plurality of baths so thatplating can be performed multiple times. The strip-shaped resin 22having a surface subjected to a conductive treatment passes through aplating bath 28 while being transferred by electrode rollers 26, whichfunction as feed rollers and power feeding cathodes on the outside ofthe bath, to thereby perform plating. The plurality of baths includeanodes 27 made of aluminum facing both faces of the resin molded bodyvia the plating bath 28, which allow more uniform plating on both facesof the resin molded body. A plating liquid is adequately removed fromthe plated aluminum porous body by nitrogen gas blowing and then thealuminum porous body is washed with water to obtain an aluminum porousbody.

On the other hand, an inorganic salt bath can also be used as a moltensalt to an extent to which a resin is not melted or the like. Theinorganic salt bath is a salt of a two-component system, typicallyAlCl₃—XCl (X: alkali metal), or a multi-component system. Such aninorganic salt bath usually has a higher molten temperature than that inan organic salt bath like an imidazolium salt bath, but it has lessenvironmental constraints such as water content or oxygen and can be putto practical use at low cost as a whole. When the resin is a melaminefoam resin, an inorganic salt bath at 60° C. to 150° C. is employedbecause the resin can be used at a higher temperature than a urethanefoam resin.

An aluminum structure having a resin molded body as the core of itsskeleton is obtained through the above-mentioned steps. For someapplications such as various filters and a catalyst support, thealuminum structure may be used as a resin-metal composite as it is, butwhen the aluminum structure is used as a metal porous body without aresin because of constraints resulting from the usage environment, theresin is removed. In the present invention, in order to avoid causingthe oxidation of aluminum, the resin is removed through decomposition ina molten salt described below.

(Removal of Resin: Treatment by Molten Salt)

The decomposition in a molten salt is performed in the following manner.A resin molded body having an aluminum plated layer formed on thesurface thereof is dipped in a molten salt, and is heated while applyinga negative potential (potential lower than a standard electrodepotential of aluminum) to the aluminum layer to remove the resin moldedbody. When the negative potential is applied to the aluminum layer withthe resin molded body dipped in the molten salt, the resin molded bodycan be decomposed without oxidizing aluminum. A heating temperature canbe appropriately selected in accordance with the type of the resinmolded body. When the resin molded body is urethane, a temperature ofthe molten salt bath needs to be 380° C. or higher since decompositionof urethane occurs at about 380° C., but the treatment needs to beperformed at a temperature equal to or lower than the melting point(660° C.) of aluminum in order to avoid melting aluminum. A preferredtemperature range is 500° C. or higher and 600° C. or lower. A negativepotential to be applied is on the minus side of the reduction potentialof aluminum and on the plus side of the reduction potential of thecation in the molten salt. In this manner, an aluminum porous body whichhas continuous pores, and has a thin oxide layer on the surface and alow oxygen content can be obtained.

The molten salt used in the decomposition of the resin may be a halidesalt of an alkali metal or alkaline earth metal such that the aluminumelectrode potential is lower. More specifically, the molten saltpreferably contains one or more salts selected from the group consistingof lithium chloride (LiCl), potassium chloride (KCl), and sodiumchloride (NaCl). In this manner, an aluminum porous body which hascontinuous pores, and has a thin oxide layer on the surface and a lowoxygen content can be obtained.

Next, a process for producing an electrode from the aluminum porous bodythus obtained will be described.

FIG. 1 is a view illustrating an example of a process for continuouslyproducing an electrode from an aluminum porous body. The processincludes a porous body sheet winding off step A of winding off a porousbody sheet from a winding off roller 41, a thickness adjustment step Busing a compressing roller 42, a lead welding step C using acompressing/welding roller 43 and a lead welding roller 49, a slurryfilling step D using a filling roller 44, a slurry supply nozzle 50 anda slurry 51, a drying step E using a drying machine 45, a compressingstep F using a compressing roller 46, a cutting step G using a cuttingroller 47, and a wind-up step H using a wind-up roller 48. Hereinafter,these steps will be described specifically.

(Thickness Adjustment Step)

An aluminum porous body sheet is wound off from a raw sheet roll aroundwhich the sheet of an aluminum porous body has been wound and isadjusted so as to have an optimum thickness and a flat surface by rollerpressing in the thickness adjustment step. The final thickness of thealuminum porous body is appropriately determined in accordance with anapplication of an electrode, and this thickness adjustment step is aprecompressing step of a compressing step for achieving the finalthickness and compresses the aluminum porous body to a level ofthickness at which a treatment in the following step is easilyperformed. A flat-plate press or a roller press is used as a pressingmachine. The flat-plate press is preferable for suppressing theelongation of a current collector, but is not suitable for massproduction, and therefore roller press capable of continuous treatmentis preferably used.

(Lead Welding Step)

—Compression of End Part of Aluminum Porous Body—

When the aluminum porous body is used as an electrode current collectorof a secondary battery or the like, a tab lead for external extractionneeds to be welded to the aluminum porous body. In the case of anelectrode using the aluminum porous body, since a robust metal part isnot present in the aluminum porous body, it is impossible to weld a leadpiece directly to the aluminum porous body. Therefore, an end part ofthe aluminum porous body is processed into the form of foil bycompressing to impart mechanical strength thereto, and a tab lead iswelded to the part.

An example of a method of processing the end part of the aluminum porousbody will be described.

FIG. 8 is a view schematically showing the compressing step.

A rotating roller can be used as a compressing jig.

When the compressed part has a thickness of about 0.05 mm or more andabout 0.2 mm or less (for example, about 0.1 mm), predeterminedmechanical strength can be achieved.

In FIG. 9, the central part of an aluminum porous body 34 having a widthof two aluminum porous bodies is compressed by a rotating roller 35 as acompressing jig to form a compressed part (lead part) 33. Aftercompression, the compressed part 33 is cut along the center line of thecentral part to obtain two sheets of electrode current collectors havinga compressed part at the end of the current collector.

Further, a plurality of current collectors can be obtained by forming aplurality of strip-shaped compressed parts at the central part of thealuminum porous body by using a plurality of rotating rollers, andcutting along the respective center lines of these strip-shapedcompressed parts.

—Bonding of Tab Lead to Peripheral Part of Electrode—

A tab lead is bonded to the compressed end part of the current collectorthus obtained. It is preferred that a metal foil is used as a tab leadin order to reduce electric resistance of an electrode and the metalfoil is bonded to the surface of at least one side of peripheries of theelectrode. Further, in order to reduce electric resistance, welding ispreferably employed as a bonding method. A width for welding a metalfoil is preferably 10 mm or less since a too wide metal foil causeswasted space to increase in a battery and a capacity density of thebattery is decreased. When the width for welding is too narrow, sincewelding becomes difficult and the effect of collecting a current isdeteriorated, the width is preferably 1 mm or more.

As a method of welding, a method of resistance welding or ultrasonicwelding can be used, but the ultrasonic welding is preferred because ofits larger bonding area.

—Metal Foil—

A material of the metal foil is preferably aluminum in consideration ofelectric resistance and tolerance for an electrolytic solution. Further,since impurities in the metal foil causes the elution or reaction of theimpurities in a battery, a capacitor or a lithium-ion capacitor, analuminum foil having a purity of 99.99% or more is preferably used. Thethickness of the welded part is preferably smaller than that of theelectrode itself.

The aluminum foil is preferably made to have a thickness of 20 to 500μm.

Welding of the metal foil may be performed before filling the currentcollector with an active material, or may be performed after thefilling, but when the welding is performed before filling, the activematerial can be prevented from exfoliating. Particularly, in the case ofultrasonic welding, welding is preferably performed before filling.Moreover, an activated carbon paste may adhere to a welded portion, butsince there is a possibility that the paste can be peeled off during thestep, the welded portion is preferably masked in order to avoid fillingthe paste.

In addition, though in the above description, the compressing step ofthe end part and the bonding step of the tab lead have been described asseparate steps, the compressing step and the bonding step may beperformed simultaneously. In this case, a roller, in which a roller partto be brought into contact, as a compressing roller, with an end partfor bonding a tab lead of the aluminum porous body sheet can performresistance welding, is used, and the aluminum porous body sheet and themetal foil can be simultaneously supplied to the roller to performcompressing of the end part and metal foil welding to the compressedpart simultaneously.

(Step of Filling Active Material)

An electrode is obtained by filling the current collector prepared asdescribed above with an active material. The active material isappropriately selected in accordance with the purpose of use of theelectrode.

For filling the active material, publicly known methods such as a methodof filling by immersion and a coating method can be employed. Examplesof the coating method include a roll coating method, an applicatorcoating method, an electrostatic coating method, a powder coatingmethod, a spray coating method, a spray coater coating method, a barcoater coating method, a roll coater coating method, a dip coatercoating method, a doctor blade coating method, a wire bar coatingmethod, a knife coater coating method, a blade coating method, and ascreen printing method.

When the active material is filled, a conduction aid or a binder isadded as required, and an organic solvent is mixed therewith to preparea slurry, and the prepared slurry is filled into the aluminum porousbody by using the above-mentioned filling method.

FIG. 10 shows a method of filling a porous body with a slurry by a rollcoating method. As shown in the figure, the slurry is supplied onto aporous body sheet and this sheet is passed between a pair of rotatingrollers opposed to each other at a predetermined interval. The slurry ispressed and filled into the porous body when passing between therotating rollers.

(Drying Step)

The porous body filled with the active material is transferred to adrying machine and heated to evaporate/remove the organic solvent andthereby an electrode material having the active material fixed in theporous body is obtained.

(Compressing Step)

The dried electrode material is compressed to a final thickness in thecompressing step. A flat-plate press or a roller press is used as apressing machine. The flat-plate press is preferable for suppressing theelongation of a current collector, but is not suitable for massproduction, and therefore roller press capable of continuous treatmentis preferably used.

A case of compressing by roller pressing is shown in the compressingstep F of FIG. 1.

(Cutting Step)

In order to improve the ability of mass production of the electrodematerial, it is preferred that the width of a sheet of the aluminumporous body is set to the width of a plurality of final products and thesheet is cut along its traveling direction with a plurality of blades toform a plurality of long sheets of electrode materials. This cuttingstep is a step of dividing a long length of electrode material into aplurality of long lengths of electrode materials.

(Winding-Up Step)

This step is a step of winding up the plurality of long sheets ofelectrode materials obtained in the above-mentioned cutting step arounda wind-up roller.

Next, applications of the electrode material obtained in theabove-mentioned step will be described.

Examples of main applications of the electrode material in which thealuminum porous body is used as a current collector include electrodesfor nonaqueous electrolyte batteries such as a lithium battery and amolten salt battery, electrodes for a capacitor, and electrodes for alithium-ion capacitor.

Hereinafter, these applications will be described.

(Lithium Battery)

Next, an electrode material for batteries using an aluminum porous bodyand a battery will be described below. For example, when the aluminumporous body is used in a positive electrode for a lithium battery(including a lithium-ion secondary battery, etc.), lithium cobalt oxide(LiCoO₂), lithium manganese oxide (LiMn₂O₄), lithium nickel dioxide(LiNiO₂) or the like is used as an active material. The active materialis used in combination with a conduction aid and a binder.

In a conventional positive electrode material for lithium batteries, anelectrode formed by applying an active material to the surface of analuminum foil is used. Though a lithium battery has a higher capacitythan a nickel hydride battery or a capacitor, a further increase incapacity is required in automobile applications. Therefore, in order toincrease a battery capacity per unit area, the application thickness ofthe active material is increased. Further, in order to effectivelyutilize the active material, the active material needs to be inelectrical contact with the aluminum foil, a current collector, andtherefore, the active material is mixed with a conduction aid to beused.

In contrast, the aluminum porous body according to the present inventionhas a high porosity and a large surface area per unit area. Thus, acontact area between the current collector and the active material isincreased, and therefore, the active material can be effectivelyutilized, the battery capacity can be improved, and the amount of theconduction aid to be mixed can be decreased. In a lithium battery, theabove-mentioned positive electrode materials are used for a positiveelectrode, and for a negative electrode, a foil, a punched metal or aporous body of copper or nickel is used as a current collector and anegative electrode active material such as graphite, lithium titaniumoxide (Li₄Ti₅O₁₂), an alloy of Sn or Si, lithium metal or the like isused. The negative electrode active material is also used in combinationwith a conduction aid and a binder.

Such a lithium battery can have an increased capacity even with a smallelectrode area and accordingly have a higher energy density than aconventional lithium battery using an aluminum foil. The effects of thepresent invention in a secondary battery has been mainly describedabove, but the effects of the present invention in a primary battery isthe same as that in the secondary battery, and a contact area isincreased when the aluminum porous body is filled with the activematerial and a capacity of the primary battery can be improved.

(Configuration of Lithium Battery)

An electrolyte used in a lithium battery includes a nonaqueouselectrolytic solution and a solid electrolyte. FIG. 11 is a verticalsectional view of a solid-state lithium battery using a solidelectrolyte. A solid-state lithium battery 60 includes a positiveelectrode 61, a negative electrode 62, and a solid electrolyte layer (SElayer) 63 disposed between both electrodes. The positive electrode 61includes a positive electrode layer (positive electrode body) 64 and acurrent collector 65 of positive electrode, and the negative electrode62 includes a negative electrode layer 66 and a current collector 67 ofnegative electrode.

As the electrolyte, a nonaqueous electrolytic solution described lateris used besides the solid electrolyte. In this case, a separator (porouspolymer film, nonwoven fabric, paper, etc.) is disposed between bothelectrodes, and both electrodes and separator are impregnated with thenonaqueous electrolytic solution.

(Active Material Filled into Aluminum Porous Body)

When an aluminum porous body is used in a positive electrode for alithium battery, a material that can extract/insert lithium can be usedas an active material, and an aluminum porous body filled with such amaterial can provide an electrode suitable for a lithium secondarybattery. As the material of the positive electrode active material, forexample, lithium cobalt oxide (LiCoO₂), lithium nickel dioxide (LiNiO₂),lithium cobalt nickel oxide (LiCo_(0.3)Ni_(0.7)O₂), lithium manganeseoxide (LiMn₂O₄), lithium titanium oxide (Li₄Ti₅O₁₂), lithium manganeseoxide compound (LiM_(y)Mn_(2-y)O₄); M=Cr, Co, Ni) or lithium acid isused. The active material is used in combination with a conduction aidand a binder. Examples of the material of the positive electrode activematerial include transition metal oxides such as conventional lithiumiron phosphate and olivine compounds which are compounds (LiFePO₄,LiFe_(0.5)Mn_(0.5)PO₄) of the lithium iron phosphate. Further, thetransition metal elements contained in these materials may be partiallysubstituted with another transition metal element.

Moreover, examples of other positive electrode active material includelithium metals in which the skeleton is a sulfide-based chalcogenidesuch as TiS₂, V₂S₃, FeS, FeS₂ or LiMS_(x) (M is a transition metalelement such as Mo, Ti, Cu, Ni, or Fe, or Sb, Sn or Pb), and a metaloxide such as TiO₂, Cr₃O₈, V₂O₅ or MnO₂. Herein, the above-mentionedlithium titanate (Li₄Ti₅O₁₂) can also be used as a negative electrodeactive material.

(Electrolytic Solution Used in Lithium Battery)

A nonaqueous electrolytic solution is used in a polar aprotic organicsolvent, and specific examples of the nonaqueous electrolytic solutioninclude ethylene carbonate, diethyl carbonate, dimethyl carbonate,propylene carbonate, γ-butyrolactone and sulfolane. As a supportingsalt, lithium tetrafluoroborate, lithium hexafluorophosphate, an imidesalt or the like is used. The concentration of the supporting saltserving as an electrolyte is preferably higher, but a supporting salthaving a concentration of about 1 mol/L is generally used since there isa limit of dissolution.

(Solid Electrolyte Filled into Aluminum Porous Body)

The aluminum porous body may be additionally filled with a solidelectrolyte besides the active material. The aluminum porous body can besuitable for an electrode for a solid-state lithium battery by fillingthe aluminum porous body with the active material and the solidelectrolyte. However, the ratio of the active material to materialsfilled into the aluminum porous body is preferably adjusted to 50 mass %or more and more preferably 70 mass % or more from the viewpoint ofensuring a discharge capacity.

A sulfide-based solid electrolyte having high lithium ion conductivityis preferably used for the solid electrolyte, and examples of thesulfide-based solid electrolyte include sulfide-based solid electrolytescontaining lithium, phosphorus and sulfur. The sulfide-based solidelectrolyte may further contain an element such as O, Al, B, Si or Ge.

Such a sulfide-based solid electrolyte can be obtained by a publiclyknown method. Examples of a method of forming the sulfide-based solidelectrolyte include a method in which lithium sulfide (Li₂S) anddiphosphorus pentasulfide (P₂S₅) are prepared as starting materials,Li₂S and P₂S₅ are mixed in proportions of about 50:50 to about 80:20 interms of mole ratio, and the resulting mixture is fused and quenched(melting and rapid quenching method) and a method of mechanicallymilling the quenched product (mechanical milling method).

The sulfide-based solid electrolyte obtained by the above-mentionedmethod is amorphous. The sulfide-based solid electrolyte can also beutilized in this amorphous state, but it may be subjected to a heattreatment to form a crystalline sulfide-based solid electrolyte. It canbe expected to improve lithium ion conductivity by this crystallization.

(Filling of Active Material into Aluminum Porous Body)

For filling the active material (active material and solid electrolyte),publicly known methods such as a method of filling by immersion and acoating method can be employed. Examples of the coating method include aroll coating method, an applicator coating method, an electrostaticcoating method, a powder coating method, a spray coating method, a spraycoater coating method, a bar coater coating method, a roll coatercoating method, a dip coater coating method, a doctor blade coatingmethod, a wire bar coating method, a knife coater coating method, ablade coating method, and a screen printing method.

When the active material (active material and solid electrolyte) isfilled, for example, a conduction aid or a binder is added as required,and an organic solvent or water is mixed therewith to prepare a slurryof a positive electrode mixture. An aluminum porous body is filled withthis slurry by the above-mentioned method. As the conduction aid, forexample, carbon black such as acetylene black (AB) or Ketjen Black (KB),or carbon fibers such as carbon nano tubes (CNT) may be used. As thebinder, for example, polyvinylidene fluoride (PVDF),polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), carboxymethylcellulose (CMC), xanthan gum and the like can be used.

The organic solvent used in preparing the slurry of a positive electrodemixture can be appropriately selected as long as it does not adverselyaffect materials (i.e., an active material, a conduction aid, a binder,and a solid electrolyte as required) to be filled into the aluminumporous body. Examples of the organic solvent include n-hexane,cyclohexane, heptane, toluene, xylene, trimethylbenzene, dimethylcarbonate, diethyl carbonate, ethyl methyl carbonate, propylenecarbonate, ethylene carbonate, butylene carbonate, vinylene carbonate,vinyl ethylene carbonate, tetrahydrofuran, 1,4-dioxane, 1,3-dioxolan,ethylene glycol, and N-methyl-2-pyrrolidone. Further, when water is usedas a solvent, a surfactant may be used for enhancing fillingperformance.

In addition, in a conventional positive electrode material for lithiumbatteries, an electrode is formed by applying an active material ontothe surface of an aluminum foil. In order to increase a battery capacityper unit area, the application thickness of the active material isincreased. Further, in order to effectively utilize the active material,the active material needs to be in electrical contact with the aluminumfoil, and therefore, the active material is mixed with a conduction aidto be used. In contrast, the aluminum porous body according to thepresent invention has a high porosity and a large surface area per unitarea. Thus, a contact area between the current collector and the activematerial is increased, and therefore, the active material can beeffectively utilized, the battery capacity can be improved, and theamount of the conduction aid to be mixed can be decreased.

(Electrode for Capacitor)

FIG. 12 is a schematic sectional view showing an example of a capacitorproduced by using the electrode material for a capacitor. An electrodematerial formed by supporting an electrode active material on analuminum porous body is disposed as a polarizable electrode 141 in anorganic electrolyte 143 partitioned with a separator 142. Thepolarizable electrode 141 is connected to a lead wire 144, and all thesecomponents are housed in a case 145. When the aluminum porous body isused as a current collector, the surface area of the current collectoris increased and a contact area between the current collector andactivated carbon as an active material is increased, and therefore, acapacitor that can realize a high output and a high capacity can beobtained.

In order to produce an electrode for a capacitor, a current collector ofthe aluminum porous body is filled with the activated carbon as anactive material. The activated carbon is used in combination with aconduction aid or a binder.

In order to increase the capacity of the capacitor, the amount of theactivated carbon as a main component is preferably in a large amount,and the amount of the activated carbon is preferably 90% or more interms of the composition ratio after drying (after removing a solvent).The conduction aid and the binder are necessary, but the amounts thereofare preferably as small as possible because they are causes of areduction in capacity and further the binder is a cause of an increasein internal resistance. Preferably, the amount of the conduction aid is10 mass % or less and the amount of the binder is 10 mass % or less.

When the surface area of the activated carbon is larger, the capacity ofthe capacitor is larger, and therefore, the activated carbon preferablyhas a specific surface area of 1000 m²/g or more. As a material of theactivated carbon, a plant-derived palm shell, a petroleum-based materialor the like may be used. In order to increase the surface area of theactivated carbon, the material is preferably activated by use of steamor alkali.

The electrode material predominantly composed of the activated carbon ismixed and stirred to obtain an activated carbon paste. This activatedcarbon paste is filled into the above-mentioned current collector anddried, and its density is increased by compressing with a roller pressor the like as required to obtain an electrode for a capacitor.

(Filling of Activated Carbon into Aluminum Porous Body)

For filling of the activated carbon, publicly known methods such as amethod of filling by immersion and a coating method can be employed.Examples of the coating method include a roll coating method, anapplicator coating method, an electrostatic coating method, a powdercoating method, a spray coating method, a spray coater coating method, abar coater coating method, a roll coater coating method, a dip coatercoating method, a doctor blade coating method, a wire bar coatingmethod, a knife coater coating method, a blade coating method, and ascreen printing method.

When the active material is filled, for example, a conduction aid or abinder is added as required, and an organic solvent or water is mixedtherewith to prepare a slurry of a positive electrode mixture. Analuminum porous body is filled with this slurry by the above-mentionedmethod. As the conduction aid, for example, carbon black such asacetylene black (AB) or Ketjen Black (KB), or carbon fibers such ascarbon nano tubes (CNT) may be used. As the binder, for example,polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE),polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), xanthan gum andthe like can be used.

The organic solvent used in preparing the slurry of a positive electrodemixture can be appropriately selected as long as it does not adverselyaffect materials (i.e., an active material, a conduction aid, a binder,and a solid electrolyte as required) to be filled into the aluminumporous body. Examples of the organic solvent include n-hexane,cyclohexane, heptane, toluene, xylene, trimethylbenzene, dimethylcarbonate, diethyl carbonate, ethyl methyl carbonate, propylenecarbonate, ethylene carbonate, butylene carbonate, vinylene carbonate,vinyl ethylene carbonate, tetrahydrofuran, 1,4-dioxane, 1,3-dioxolan,ethylene glycol, and N-methyl-2-pyrrolidone. Further, when water is usedas a solvent, a surfactant may be used for enhancing fillingperformance.

(Preparation of Capacitor)

The electrode obtained in the above-mentioned manner is punched out intoan appropriate size to prepare two sheets, and these two electrodes areopposed to each other with a separator interposed therebetween. A porousfilm or nonwoven fabric made of cellulose or a polyolefin resin ispreferably used for the separator. Then, the electrodes are housed in acell case by use of required spacers, and impregnated with anelectrolytic solution. Finally, a lid is put on the case with aninsulating gasket interposed between the lid and the case and is sealed,and thereby an electric double layer capacitor can be prepared. When anonaqueous material is used, materials of the electrode and the like arepreferably adequately dried for decreasing the water content in thecapacitor as much as possible. Preparation of the capacitor is performedin low-moisture environments, and sealing may be performed inreduced-pressure environments. In addition, the capacitor is notparticularly limited as long as the current collector and the electrodeof the present invention are used, and capacitors may be used which areprepared by a method other than this method.

Though as the electrolytic solution, both an aqueous system and anonaqueous system can be used, the nonaqueous system is preferably usedsince its voltage can be set at a higher level than that of the aqueoussystem. In the aqueous system, potassium hydroxide or the like can beused as an electrolyte. Examples of the nonaqueous system include manyionic liquids in combination of a cation and an anion. As the cation,lower aliphatic quaternary ammonium, lower aliphatic quaternaryphosphonium, imidazolium or the like is used, and as the anion, ions ofmetal chlorides, ions of metal fluorides, and imide compounds such asbis(fluorosulfonyl)imide and the like are known. Further, as thenonaqueous system, there is a polar aprotic organic solvent, andspecific examples thereof include ethylene carbonate, diethyl carbonate,dimethyl carbonate, propylene carbonate, γ-butyrolactone and sulfolane.As a supporting salt in the nonaqueous electrolytic solution, lithiumtetrafluoroborate, lithium hexafluorophosphate or the like is used.

(Lithium-Ion Capacitor)

FIG. 13 is a schematic sectional view showing an example of alithium-ion capacitor produced by using the electrode material for alithium-ion capacitor. In an organic electrolytic solution 143partitioned with a separator 142, an electrode material formed bysupporting a positive electrode active material on an aluminum porousbody is disposed as a positive electrode 146 and an electrode materialformed by supporting a negative electrode active material on a currentcollector is disposed as a negative electrode 147. The positiveelectrode 146 and the negative electrode 147 are connected to a leadwire 148 and a lead wire 149, respectively, and all these components arehoused in a case 145. When the aluminum porous body is used as a currentcollector, the surface area of the current collector is increased, andtherefore, even when activated carbon as an active material is appliedonto the aluminum porous body in a thin manner, a capacitor that canrealize a high output and a high capacity can be obtained.

(Positive Electrode)

In order to produce an electrode for a lithium-ion capacitor, a currentcollector of the aluminum porous body is filled with activated carbon asan active material. The activated carbon is used in combination with aconduction aid or a binder.

In order to increase the capacity of the lithium-ion capacitor, theamount of the activated carbon as a main component is preferably in alarge amount, and the amount of the activated carbon is preferably 90%or more in terms of the composition ratio after drying (after removing asolvent). The conduction aid and the binder are necessary, but theamounts thereof are preferably as small as possible because they arecauses of a reduction in capacity and further the binder is a cause ofan increase in internal resistance. Preferably, the amount of theconduction aid is 10 mass % or less and the amount of the binder is 10mass % or less.

When the surface area of the activated carbon is larger, the capacity ofthe lithium-ion capacitor is larger, and therefore, the activated carbonpreferably has a specific surface area of 1000 m²/g or more. As amaterial of the activated carbon, a plant-derived palm shell, apetroleum-based material or the like may be used. In order to increasethe surface area of the activated carbon, the material is preferablyactivated by use of steam or alkali. As the conduction aid, KetjenBlack, acetylene black, carbon fibers or composite materials thereof maybe used. As the binder, polyvinylidene fluoride,polytetrafluoroethylene, polyvinyl alcohol, carboxymethyl cellulose,xanthan gum and the like can be used. A solvent may be appropriatelyselected from water and an organic solvent depending on the type of thebinder. In the organic solvent, N-methyl-2-pyrrolidone is often used.Further, when water is used as a solvent, a surfactant may be used forenhancing filling performance.

The electrode material predominantly composed of the activated carbon ismixed and stirred to obtain an activated carbon paste. This activatedcarbon paste is filled into the above-mentioned current collector anddried, and its density is increased by compressing with a roller pressor the like as required to obtain an electrode for a lithium-ioncapacitor.

(Filling of Activated Carbon into Aluminum Porous Body)

For filling of the activated carbon, publicly known methods such as amethod of filling by immersion and a coating method can be employed.Examples of the coating method include a roll coating method, anapplicator coating method, an electrostatic coating method, a powdercoating method, a spray coating method, a spray coater coating method, abar coater coating method, a roll coater coating method, a dip coatercoating method, a doctor blade coating method, a wire bar coatingmethod, a knife coater coating method, a blade coating method, and ascreen printing method.

When the active material is filled, for example, a conduction aid or abinder is added as required, and an organic solvent or water is mixedtherewith to prepare a slurry of a positive electrode mixture. Analuminum porous body is filled with this slurry by the above-mentionedmethod. As the conduction aid, for example, carbon black such asacetylene black (AB) or Ketjen Black (KB), or carbon fibers such ascarbon nano tubes (CNT) may be used. As the binder, for example,polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE),polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), xanthan gum andthe like can be used.

The organic solvent used in preparing the slurry of a positive electrodemixture can be appropriately selected as long as it does not adverselyaffect materials (i.e., an active material, a conduction aid, a binder,and a solid electrolyte as required) to be filled into the aluminumporous body. Examples of the organic solvent include n-hexane,cyclohexane, heptane, toluene, xylene, trimethylbenzene, dimethylcarbonate, diethyl carbonate, ethyl methyl carbonate, propylenecarbonate, ethylene carbonate, butylene carbonate, vinylene carbonate,vinyl ethylene carbonate, tetrahydrofuran, 1,4-dioxane, 1,3-dioxolan,ethylene glycol, and N-methyl-2-pyrrolidone. Further, when water is usedas a solvent, a surfactant may be used for enhancing fillingperformance.

(Negative Electrode)

A negative electrode is not particularly limited and a conventionalnegative electrode for lithium batteries can be used, but an electrode,in which an active material is filled into a porous body made of copperor nickel like the foamed nickel described above, is preferable becausea conventional electrode, in which a copper foil is used for a currentcollector, has a small capacity. Further, in order to perform theoperations as a lithium-ion capacitor, the negative electrode ispreferably doped with lithium ions in advance. As a doping method,publicly known methods can be employed. Examples of the doping methodsinclude a method in which a lithium metal foil is affixed to the surfaceof a negative electrode and this is dipped into an electrolytic solutionto dope it, a method in which an electrode having lithium metal fixedthereto is arranged in a lithium-ion capacitor, and after assembling acell, an electric current is passed between the negative electrode andthe lithium metal electrode to electrically dope the electrode, and amethod in which an electrochemical cell is assembled from a negativeelectrode and lithium metal, and a negative electrode electrically dopedwith lithium is taken out and used.

In any method, it is preferred that the amount of lithium-doping islarge in order to adequately decrease the potential of the negativeelectrode, but the negative electrode is preferably left without beingdoped by the capacity of the positive electrode because when theresidual capacity of the negative electrode is smaller than that of thepositive electrode, the capacity of the lithium-ion capacitor becomessmall.

(Electrolytic Solution Used in Lithium-Ion Capacitor)

The same nonaqueous electrolytic solution as that used in a lithiumbattery is used for an electrolytic solution. A nonaqueous electrolyticsolution is used in a polar aprotic organic solvent, and specificexamples of the nonaqueous electrolytic solution include ethylenecarbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate,γ-butyrolactone and sulfolane. As a supporting salt, lithiumtetrafluoroborate, lithium hexafluorophosphate, an imide salt or thelike is used.

(Preparation of Lithium-Ion Capacitor)

The electrode obtained in the above-mentioned manner is punched out intoan appropriate size, and is opposed to the negative electrode with aseparator interposed between the punched out electrode and the negativeelectrode. The negative electrode may be an electrode doped with lithiumions by the above-mentioned method, and when the method of doping thenegative electrode after assembling a cell is employed, an electrodehaving lithium metal connected thereto may be arranged in the cell. Aporous film or nonwoven fabric made of cellulose or a polyolefin resinis preferably used for the separator. Then, the electrodes are housed ina cell case by use of required spacers, and impregnated with anelectrolytic solution. Finally, a lid is put on the case with aninsulating gasket interposed between the lid and the case and is sealed,and thereby a lithium-ion capacitor can be prepared. Materials of theelectrode and the like are preferably adequately dried for decreasingthe water content in the lithium ion capacitor as much as possible.Preparation of the lithium ion capacitor is performed in low-moistureenvironments, and sealing may be performed in reduced-pressureenvironments. In addition, the lithium ion capacitor is not particularlylimited as long as the current collector and the electrode of thepresent invention are used, and capacitors may be used which areprepared by a method other than this method.

(Electrode for Molten Salt Battery)

The aluminum porous body can also be used as an electrode material formolten salt batteries. When the aluminum porous body is used as apositive electrode material, a metal compound such as sodium chromite(NaCrO₂) or titanium disulfide (TiS₂) into which a cation of a moltensalt serving as an electrolyte can be intercalated is used as an activematerial. The active material is used in combination with a conductionaid and a binder. As the conduction aid, acetylene black or the like maybe used. As the binder, polytetrafluoroethylene (PTFE) and the like maybe used. When sodium chromite is used as the active material andacetylene black is used as the conduction aid, the binder is preferablyPTFE because PTFE can tightly bind sodium chromite and acetylene black.

The aluminum porous body can also be used as a negative electrodematerial for molten salt batteries. When the aluminum porous body isused as a negative electrode material, sodium alone, an alloy of sodiumand another metal, carbon, or the like may be used as an activematerial. Sodium has a melting point of about 98° C. and a metal becomessofter with an increase in temperature. Thus, it is preferable to alloysodium with another metal (Si, Sn, In, etc.). In particular, an alloy ofsodium and Sn is preferred because of its easiness of handleability.Sodium or a sodium alloy can be supported on the surface of the aluminumporous body by electroplating, hot dipping, or another method.Alternatively, a metal (Si, etc.) to be alloyed with sodium may bedeposited on the aluminum porous body by plating and then converted intoa sodium alloy by charging in a molten salt battery.

FIG. 14 is a schematic sectional view showing an example of a moltensalt battery in which the above-mentioned electrode material forbatteries is used. The molten salt battery includes a positive electrode121 in which a positive electrode active material is supported on thesurface of an aluminum skeleton of an aluminum porous body, a negativeelectrode 122 in which a negative electrode active material is supportedon the surface of an aluminum skeleton of an aluminum porous body, and aseparator 123 impregnated with a molten salt of an electrolyte, whichare housed in a case 127. A pressing member 126 including a presserplate 124 and a spring 125 for pressing the presser plate is arrangedbetween the top surface of the case 127 and the negative electrode. Byproviding the pressing member, the positive electrode 121, the negativeelectrode 122 and the separator 123 can be evenly pressed to be broughtinto contact with one another even when their volumes have been changed.A current collector (aluminum porous body) of the positive electrode 121and a current collector (aluminum porous body) of the negative electrode122 are connected to a positive electrode terminal 128 and a negativeelectrode terminal 129, respectively, through a lead wire 130.

The molten salt serving as an electrolyte may be various inorganic saltsor organic salts which melt at the operating temperature. As a cation ofthe molten salt, one or more cations selected from alkali metals such aslithium (Li), sodium (Na), potassium (K), rubidium (Rb) and cesium (Cs),and alkaline earth metals such as beryllium (Be), magnesium (Mg),calcium (Ca), strontium (Sr) and barium (Ba) may be used.

In order to decrease the melting point of the molten salt, it ispreferable to use a mixture of at least two salts. For example, use ofpotassium bis(fluorosulfonyl)amide (K—N(SO₂F)₂; KFSA) and sodiumbis(fluorosulfonyl)amide (Na—N(SO₂F)₂; NaFSA) in combination candecrease the battery operating temperature to 90° C. or lower.

The molten salt is used in the form of a separator impregnated with themolten salt. The separator prevents the contact between the positiveelectrode and the negative electrode, and may be a glass nonwovenfabric, a porous resin molded body or the like. A laminate of thepositive electrode, the negative electrode, and the separatorimpregnated with the molten salt housed in a case is used as a battery.

EXAMPLES

Hereinafter, the present invention will be described in more detailbased on examples, but the present invention is not limited thereto.

Example 1 Formation of Conductive Layer

A urethane foam having a porosity of 95%, about 46 pores (cells) perinch, a pore diameter of about 550 μm, and a thickness of 1 mm wasprepared as a resin molded body and was cut into a 100 mm×30 mm square.A film of aluminum was formed on the surface of the polyurethane foam ina weight per unit area of 10 g/m² by sputtering to form a conductivelayer.

(Molten Salt Plating)

The urethane foam having a conductive layer formed on the surfacethereof was loaded as a piece of work in a jig having an electricitysupply function, and then the jig was placed in a glove box, theinterior of which was adjusted to an argon atmosphere and low moisture(a dew point of −30° C. or lower), and was dipped in a molten saltaluminum plating bath (33 mol % EMIC-67 mol % AlCl₃) at a temperature of40° C. The jig holding the piece of work was connected to the cathode ofa rectifier, and an aluminum plate (purity 99.99%) of the counterelectrode was connected to the anode. The piece of work was plated byapplying a direct current at a current density of 3.6 A/dm² for 90minutes to obtain an aluminum structure in which 140 g/m² of an aluminumplated layer was formed on the surface of the urethane foam. Stirringwas performed with a stirrer using a Teflon (registered trademark)rotor. Here, the current density was calculated based on the apparentarea of the urethane foam.

(Decomposition of Resin Molded Body)

Each of the above-mentioned aluminum structures was dipped in a LiCl—KCleutectic molten salt at a temperature of 500° C., and a negativepotential of −1 V was applied to the aluminum structure for 30 minutes.Air bubbles resulting from the decomposition reaction of thepolyurethane were generated in the molten salt. Then, the aluminumstructure was cooled to room temperature in the atmosphere and waswashed with water to remove the molten salt, to obtain an aluminumporous body from which the resin had been removed. The obtained aluminumporous body had continuous pores and a high porosity as with theurethane foam used as a core material.

(Processing of End Part of Aluminum Porous Body)

The thickness of the obtained aluminum porous body was adjusted to 0.96mm by roller pressing, and the aluminum porous body was cut into a pieceof 5 cm square.

As preparation of welding, SUS blocks (rods) each having a width of 5 mmand a hammer were used as a compressing jig, and a location 5 mm fromone end of the aluminum porous body was sandwiched between the SUSblocks, and the aluminum porous body was compressed by beating the SUSblocks with the hammer to form a compressed part having a thickness of100 μm.

Thereafter, a tab lead was welded by spot welding under the followingconditions.

<Welding Condition>

Welding apparatus: Hi-Max 100 manufactured by Panasonic Corporation,model No. YG-101 UD

-   -   (Voltage can be applied up to 250 V)    -   Capacity: 100 Ws, 0.6 kVA

Electrode: Copper electrode of 2 mm in diameter

Load: 8 kgf

Voltage: 140 V

<Tab Lead>

Material: aluminum

Dimension: width 5 mm, length 7 cm, thickness 100 μm

Surface condition: boehmite treatment

The tensile strength of the obtained aluminum porous body was measuredby a tensile test (test piece: 10 mm wide and 100 mm long, distancebetween chucks: 50 mm) to find that it was 0.6 MPa, and it was confirmedthat the aluminum porous body can endure the industrial continuousproduction of an electrode.

Further, the average crystal grain size of the obtained aluminum porousbody was measured to find that it was 3 μm. Moreover, the carbon contentwas measured by a high-frequency combustion-infrared absorption methodto find that it was 0.8 g/m².

Example 2

An aluminum porous body was obtained in the same manner as in Example 1except for plating the piece of work by applying a direct current at acurrent density of 7.2 A/dm² for 90 minutes in the molten salt platingof Example 1 to form 280 g/m² of an aluminum-plated layer on the surfaceof the urethane foam.

The tensile strength of the obtained aluminum porous body was measuredin the same manner as in Example 1 to find that it was 1.2 MPa. Further,the average crystal grain size was 2 μm and the carbon content was 0.9g/m².

Example 3

An aluminum porous body was obtained in the same manner as in Example 1except for employing the following method as a method of conductivetreatment in Example 1.

(Method of Conductive Treatment)

One hundred g of carbon black, which is amorphous carbon having aparticle diameter of 0.01 to 0.2 μm, was dispersed in 0.5 L of a 10%aqueous acrylic ester-based resin solution to prepare a sticky coatingmaterial in this ratio. Next, a conductive treatment was performed bycontinuously immersing a porous resin sheet in the above-mentionedcoating material, squeezing the porous resin sheet with a roller anddrying the sheet to form a conductive coating layer on the surface ofthe three-dimensional network resin.

The tensile strength of the obtained aluminum porous body was measuredin the same manner as in Example 1 to find that it was 0.5 MPa. Further,the average crystal grain size was 2 μm and the carbon content was 10g/m².

The present invention has been described based on embodiments, but it isnot limited to the above-mentioned embodiments. Variations to theseembodiments may be made within the scope of identity and equivalence ofthe present invention.

INDUSTRIAL APPLICABILITY

Since the three-dimensional network aluminum porous body of the presentinvention is in a long sheet-shaped state and excellent in tensilestrength, it can be suitably used as a base material in performingindustrial continuous production of electrodes for a nonaqueouselectrolyte battery (lithium battery, etc.), a capacitor and alithium-ion capacitor.

REFERENCE SIGNS LIST

-   -   1 Resin molded body    -   2 Conductive layer    -   3 Aluminum-plated layer    -   11 Strip-shaped resin    -   12 Supply bobbin    -   13 Deflector roll    -   14 Suspension liquid of conductive coating material    -   15 Bath    -   16 Hot air nozzle    -   17 Squeezing roll    -   18 Take-up bobbin    -   21 a, 21 b Plating bath    -   22 Strip-shaped resin    -   23, 28 Plating bath    -   24 Cylindrical electrode    -   25, 27 Anode    -   26 Electrode roller    -   32 Compressing jig    -   33 Compressed part    -   34 Aluminum porous body    -   35 Rotating roller    -   36 Rotation axis of roller    -   37 Tab lead    -   38 Insulating/sealing tape    -   41 Winding off roller    -   42 Compressing roller    -   43 Compressing-welding roller    -   44 Filling roller    -   45 Drying machine    -   46 Compressing roller    -   47 Cutting roller    -   48 Wind-up roller    -   49 Lead supply roller    -   50 Slurry supply nozzle    -   51 Slurry    -   60 Lithium battery    -   61 Positive electrode    -   62 Negative electrode    -   63 Electrolyte layer    -   64 Positive electrode layer (positive electrode body)    -   65 Current collector of positive electrode    -   66 Negative electrode layer    -   67 Current collector of negative electrode    -   121 Positive electrode    -   122 Negative electrode    -   123 Separator    -   124 Presser plate    -   Spring    -   126 Pressing member    -   127 Case    -   128 Positive electrode terminal    -   129 Negative electrode terminal    -   130 Lead wire    -   141 Polarizable electrode    -   142 Separator    -   143 Organic electrolytic solution    -   144 Lead wire    -   145 Case    -   146 Positive electrode    -   147 Negative electrode    -   148 Lead wire    -   149 Lead wire

The invention claimed is:
 1. A continuous three-dimensional networkaluminum porous body comprising: a long sheet-shaped continuousthree-dimensional network aluminum porous body, the continuousthree-dimensional network aluminum porous body having a tensile strengthranging from 0.2 to 5 MPa, wherein the continuous three-dimensionalnetwork aluminum porous body comprises an electroplated aluminumconstituted of a plurality of crystals having an average crystal grainsize ranging from 2 to 10 μm.
 2. The three-dimensional network aluminumporous body according to claim 1, wherein the three-dimensional networkaluminum porous body contains carbon in an amount ranging from 0.05 to20 g/m².